What is JEB?

Junctional epidermolysis bullosa (JEB) is an inherited disease that causes moderate to severe blistering of the skin and mouth epithelia, and sloughing of hooves in newborn Belgian foals. Affected foals are typically born alive, but soon develop skin lesions at pressure points which worsen with time, and the foal eventually succumbs from severe infection or has to be euthanized.

JEB in Belgian horses has been shown to be the result of a specific mutation in a gene that affects the production of normal and healthy skin. In addition to Belgians, this mutation has been found in American Creams, Bretons, Comtois and American Saddlebreds.

JEB is inherited as a recessive trait. Animals that carry two copies of the mutated gene (homozygous recessive) will develop the disease. Animals that carry one copy of the mutated gene and one copy of the normal gene (heterozygous) are carriers of JEB. Carriers do not develop the disease and have normal epithelia, but they have a 50% chance of passing on the mutation to their offspring.

The history of JEB:

Scientific reports of this condition date back to 1934 in Sweden, 1936 in the Netherlands and 28 cases reported in Germany from 1935 to 1944. The condition is not only isolated to the Belgian horse but similar conditions are also reported in the American Saddlebred and even humans. It was through the human research being conducted by the French, in collaboration with Dr. John D. Baird of the University of Guelph, Ontario, Canada, whereby the gene site of the mutation was isolated on January 24, 2002. This breakthrough removed the single largest obstacle to developing a test to identify our carrier and non-carrier horses.

How do I identify if a foal has JEB?

This genetic mutation results in the defective production of a skin protein that holds the skin to the body. The foals are typically born alive and well, but soon develop patches of hair and skin loss over points of wear. These patches soon become larger and encompass large areas of the foal’s body. Hoof attachment is also dependent on this protein and with its absence, leads to the loss of the hoof wall. The foal generally dies or is euthanized due to severe infection and discomfort at 3 to 8 days of age. JEB foals also have their front teeth at birth, coupled with oral ulcers.

How do genetics work in regards to this mutation?

There are three possible genetic outcomes involving this mutation:

  1. Lethal JEB foals: these horses die shortly after birth and, obviously, never reproduce.
  2. Carriers: these horses carry the genetic mutation and it is the breeding of two carrier
    horses that allows the birth of a JEB foal. Breeding two carrier horses results in the following outcomes:
    • 25% Non-carrier offspring (N/N)
    • 50% Carrier offspring (N/J)
    • 25% Lethal JEB foals (J/J)
  3. Non-carriers: these horses do not carry the genetic mutation and the breeding of two
    non-carrier horses results in all their offspring being non-carriers. The breeding of a non-carrier
    to a carrier results in the following outcomes:
    • 50% Non-carrier offspring (N/N)
    • 50% Carrier offspring (N/J)

Breeders can reliably use test results to enhance breeding strategies to avoid producing affected foals. Carriers do not need to be removed from the breeding pool. A successful breeding program can use matings of carriers (N/J) to non-carriers (N/N) without the worry of producing an affected foal.

How do I know if any of my horses are carriers?

We no longer have to guess if our animals are carriers and hope that we don’t produce a lethal JEB foal. The Belgian Corporation has contracted with the Veterinary Genetics Lab at the University of California-Davis to handle the genetic testing for JEB, as well as for our parentage verification. To complete the testing, the owner of the horse submits the registration papers and appropriate fees to the Belgian Corporation office requesting the JEB test. The Corporate office will then send back to the owner bar-coded DNA paperwork and a pre-addressed envelope. Mane and/or tail hairs of the appropriate horse are pulled and sent to UC-Davis, along with the corresponding paperwork to UC-Davis. These hairs must be pulled and not cut, so as to include the roots. If the horse is less than 1 year of age, it is recommended that you pull tail hairs and if greater than 1 year old, that you pull mane hairs. Approximately 50 hairs are required for the test.

The roots (bulb) of the hair are what contain the DNA needed for the testing. These hairs can be pulled by the owner of the horse and do not require a veterinarian. The hair samples are very stable and do not require refrigeration or special express mailing. The lab will then do the genetic testing to determine the carrier or non-carrier status along with parentage verification to confirm it was the animal specified. The results will then be returned to the Belgian office and printed on the registration papers as “carrier of JEB” or “non-carrier of JEB”. The registration papers will then be delivered to the owner.

Has the Belgian Draft Horse Corporation made this test mandatory?

The test is mandatory for all breeding stallions only, and is optional for mares. As of November 1, 2002, all sires entering into service must be/must have been JEB-tested with subsequent results printed on the certificate of registry, or be identified as a “Parentage Verified JEB Non-Carrier.” “Parentage Verified JEB Non-Carrier” will be documented on the certificate of registration provided the foal is DNA tested and one of the following conditions is met:

  1. Both parents are JEB tested Non-Carriers.

  2. One parent is a JEB tested Non-Carrier and one parent is a Parentage Verified JEB Non-Carrier.

  3. Both parents are Parentage Verified JEB Non-Carriers.

How much do the tests cost?

The DNA & JEB test for stallions is $95 per animal (or $75 for stud colts at the time of registration) and $75 for mares. All sires of foals must also be DNA profiled. All mares foaled in 2015 and after must be DNA profiled at the time of registration. The cost the DNA profile only (no JEB) is $30 per animal. These tests must be done through the Corporation, at the Corporation approved laboratory, with all fees paid in advance. DNA information can then be found on the registration application and fee schedule.

DNA Testing:

All sires of foals must be DNA profiled. All mares foaled in 2015 and after must be DNA profiled at the time of registration. These tests must be done through the Corporation, at the Corporation approved laboratory, with all fees paid in advance. DNA information can be found on the registration application and fee schedule. The DNA bar-coded paperwork and an envelope is sent to the owner after the application and fees are received.